In order to enable desktop and other computers to rapidly and directly perform newly developed technology, like high-resolution graphics function, wireless communcation etc., add-on units including “graphics cards” or “video graphic array (VGA) cards” are often installed in computer devices to permit these computer devices enhancing their operative abilities. Using graphics cards as an example, such cards include a separate processor, called a graphic processing unit (GPU), one or more memory chips and other required circuitry, all mounted to a circuit board. These electronic components, especially GPU, on such cards often have extremely large computing power and, as a consequence, generate substantial heat that if not efficiently dissipated will adversely affect normal operation of the graphics cards. Thus, a heat dissipation device is often attached to a top surface of a GPU to remove heat therefrom.
Currently, heat pipe type heat dissipation devices which have good heat transfer performance have been widely used. A heat pipe is a closed, constant mass cooling system in which the working liquid coexists in equilibrium with its vapor during the normal operating status of the heat pipe. It consists of an evaporative section, in which the working liquid is heated and vaporized; an adiabatic section, in which both vapor and condensed liquid flow with no heat being externally transferred; and a condensative section, in which vapor is condensed to liquid and the released latent heat of vaporization is transferred to the external surroundings. The liquid flows via capillary action back the evaporative section. The axial flow of the vapor and the capillary flow of the returning working liquid are both produced by pressure gradients. When the heat pipe is too long, the pressure gradient of the heat pipe will be reduced accordingly. It is then difficult for working fluid in the heat pipe to return back to the evaporative section from the condensative section. Heat transfer capability of the heat pipe will be reduced.
FIG. 6 shows a conventional heat pipe type heat dissipation device mounted on a VGA card 10. The heat dissipation device comprises a first heat sink 18, a second heat sink 20, and a heat pipe 22. In assembly, the heat pipe 22 is fixed to the the first and second heat sinks 18, 20 simultaneously by soldering or other means. The combined heat sinks 18, 20 and heat pipe 22 is then attached to the card 10. The first heat sink 18 is mounted on one side of the card 10 and directly contacts a GPU (not visible) of the card 10. The second heat sink 20 is mounted on an opposite side of the card 10. The heat pipe 22 is connected between the first and second heat sinks 18, 20 for transferring heat from the first heat sink 18 to the second heat sink 20.
However, when the two heat sinks 18, 20 are fixed to the heat pipe 22, it is difficult to position the heat sinks 18, 20 to the heat pipe 22 simultaneously. Moreover, the length of this kind of heat sinks 18, 20 is usually greater than 100 mm and the length of the heat pipe 22 is consequently greater than 200 mm, which results in heat transfer capability of the heat pipe 22 reduced since it is difficult for working fluid in the heat pipe 22 to successfully circulating in the heat pipe 22 as mentioned above. Therefore, heat dissipation efficiency of the heat dissipation device is limited.